1. Field of the Invention
The present invention relates to a non-contact type portable carrier and a method of initializing the same. More particularly, the present invention relates to a non-contact type portable carrier to which a power-supply voltage is supplied from a terminal unit by electromagnetic coupling and to a method of initializing the carrier.
2. Description of the Related Art
FIG. 5 shows the construction of a conventional non-contact type portable carrier (hereinafter referred to as an IC card) employing electromagnetic coupling. An IC card 3 has a coil 4 which is electromagnetically connected to a coil 2 of a terminal unit 1. A rectifying circuit 5 for full-wave rectifying AC power is connected to the coil 4. Connected to the rectifying circuit 5 are a capacitor 6 for smoothing pulsating current waveforms, a waveform shaping circuit 7 for detecting and shaping clock signals from AC waves, and a level detection circuit 8 for extracting signals from full-wave rectified waves. A processing circuit 11 is connected to the rectifying circuit 5, the waveform shaping circuit 7 and the level detection circuit 8 via signal lines 15, 14 and 10, respectively. Reference numerals 9a, 9b and 9c denote respective resistors for supplying bias and signal voltages to the level detection circuit 8.
A transistor 12 and an adjustment resistor 13 are connected in series between both ends of the coil 4. A signal output terminal of the processing circuit 11 is connected to the gate of the transistor 12. In addition, the IC card 3 has a reset coil 17 which is electromagnetically connected to a reset coil 16 of the terminal unit 1. A reset terminal RE of the processing circuit 11 is connected to the reset coil 17 via a waveform shaping circuit 18. Reference numeral 19 denotes a capacitor for smoothing a reset signal induced in the reset coil 17.
The operation of the conventional IC card 3 will now be explained with reference to the flowchart of FIG. 6. First, the IC card 3 is inserted into the terminal unit 1, and the coil 4 of the IC card 3 approaches the coil 2 of the terminal unit 1. In this condition, when supplying of power is started from the terminal unit 1 in step S1, power is induced in the coil 4 of the IC card 3 by electromagnetic induction, thus activating the IC card 3. Next, the terminal unit 1 sends out a reset signal to the IC card 3 from the reset coil 16 in order to initialize the processing circuit 11. The reset signal is input to the processing circuit 11 via the reset coil 17 and the waveform shaping circuit 18 of the IC card 3. In the IC card 3, if it is confirmed in step S2 that the reset signal is being received, the process proceeds to step S3 where the processing circuit 11 is initialized.
Thereafter, when the signal is sent from the terminal unit 1 via the coil 2, the process proceeds from step S2 to step S4 where the IC card 3 receives a signal. The signal detected by the level detection circuit 8 is input to the processing circuit 11. In step S5, the received signal is processed and evaluated by the processing circuit 11. In step S6, the processing circuit 11 sends out the result of the processed signal to the terminal unit 1 by controlling, i.e., turning on and off the transistor 12. When it is determined in the following step S7 that a series of transmissions and receptions of signals between the processing circuit 11 and the terminal unit 1 has been terminated, the IC card 3 receives a reset signal from the terminal unit 1 in step S8. Thereupon, the processing circuit 11 is initialized in step S9, and all processes are terminated.
However, in the conventional IC card 3, there is a problem in that the IC card 3 cannot be made smaller because the reset coil 17 must be provided separately from the coil 4 for receiving power and signals. In addition, since a dedicated reset signal must be sent from the terminal unit 1 in order to initialize the processing circuit 11 of the IC card 3, protocols for signal transmission by the terminal unit 1 become complicated.